MC68HC11KA4TS Datasheet, PDF (49/68 Pages) Motorola, Inc – 8-Bit Microcontroller

Pins AV_DD and AV_SS provide the supply voltage to the digital portion of the A/D converter. Pins V_RH and
V_RL provide the reference supply voltage inputs.
A multiplexer allows the single A/D converter to select one of 16 analog input signals. Refer to the A/D
converter channel assignment bits CD–CA description.
The A/D converter control logic implements automatic conversion sequences on a selected channel
four times or on a group of four channels once each. A write to the ADCTL register initiates conversions
and, if made while a conversion is in process, a write to ADCTL also halts a conversion operation in
progress.
When the MULT bit is zero, the A/D converter system is configured to perform four consecutive conver-
sions on the single channel specified by the four channel-select bits (CD–CA). When the MULT bit is
one, the A/D system is configured to perform conversions on each channel in the group of four channels
specified by the CD and CC channel select bits. Refer to Table 8.
When the SCAN bit is zero, four conversions are performed in the desired channel group, once each,
to fill the four result registers. When SCAN is one, conversions continue channel-by-channel in the de-
sired group with the result registers being updated continually as new data becomes available.
E CLOCK
12 E CYCLES
SAMPLE ANALOG INPUT
MSB
4
CYCLES
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 LSB 2
2
2
2
2
2
2
2 CYC
CYC CYC CYC CYC CYC CYC CYC END
SUCCESSIVE APPROXIMATION SEQUENCE
CONVERT FIRST
CONVERT SECOND
CONVERT THIRD
CONVERT FOURTH
CHANNEL, UPDATE
CHANNEL, UPDATE
CHANNEL, UPDATE
CHANNEL, UPDATE
0
ADR1
32
ADR2
64
ADR3
96
ADR4
128 — E CYCLES
Figure 15 Timing Diagram for a Sequence of Four A/D Conversions
A/D CONVERSION TIM
ANALOG
INPUT
PIN
< 2 pF
+ ~20V
– ~0.7V
INPUT
PROTECTION
DEVICE
+ ~12V
– ~0.7V
DUMMY N-CHANNEL
OUTPUT DEVICE
DIFFUSION/POLY
COUPLER
≤ 4 KΩ
400 nA
JUNCTION
LEAKAGE
*
~ 20 pF
DAC
CAPACITANCE
V_RL
* THIS ANALOG SWITCH IS CLOSED ONLY DURING THE 12-CYCLE SAMPLE TIME.
ANALOG INPUT PIN
Figure 16 Electrical Model of an Analog Input Pin (Sample Mode)
MC68HC11KA4
MC68HC11KA4TS/D
MOTOROLA
49